The soy protein isolate produced therein has a unique combination of parameters not found in other soy isolates: The product is completely soluble at acid pH values of less than about 4.4 and solutions thereof are heat stable in this pH range, permitting thermal processing, such as hot fill applications. No stabilizers or other additives are necessary to maintain the protein in solution or suspension. The soy protein isolate has no “beany” flavour and no off odours. The product is low in phytic acid and no enzymes are required in the production of the soy protein isolate. The soy protein isolate is also highly soluble at about pH 7.
The novel soy protein isolate having a soy protein content of at least about 90 wt %, preferably at least about 100 wt %, (N×6.25) on a dry weight basis (d.b.), is produced by a method which comprises:
(a) extracting a soy protein source with an aqueous calcium salt solution, particularly calcium chloride solution, to cause solubilization of soy protein from the protein source and to form an aqueous soy protein solution,
(b) separating the aqueous soy protein solution from residual soy protein source,
(c) optionally diluting the aqueous soy protein solution,
(d) adjusting the pH of the aqueous soy protein solution to a pH of about 1.5 to about 4.4, preferably about 2 to about 4, to produce an acidified clear soy protein solution,
(e) optionally heat treating the acidified solution to reduce the activity of anti-nutritional trypsin inhibitors and the microbial load,
(f) optionally concentrating the aqueous clear soy protein solution while maintaining the ionic strength, substantially constant by using a selective membrane technique,
(g) optionally diafiltering the concentrated soy protein solution,
(h) optionally pasteurizing the concentrated soy protein solution to reduce the microbial load, and
(i) optionally drying the concentrated soy protein solution.